Scheme to prevent HFN un-synchronization for UM RLC in a high speed wireless communication system

ABSTRACT

When the system receives a request to switch for using a smaller TBS size, instead of discarding the unacknowledged MAC-hs PDUs, this invention will pick up RLC UM PDUs or RLC AM PDUs or both of them from the unacknowledged MAC-hs PDUs affected by the size change request and reload them into the new PDU. Meantime, this invention will select RLC UM PDUs over RLC AM PDUs to load into the new PDU if the unacknowledged MAC-hs PDU contains both of them. Therefore, this invention reduces the risk of loss of synchronization for UM RLC because the discarding of unacknowledged MAC-hs PDUs according to the prior art.

CROSS REFERENCE APPLICATION

This application claims priority from U.S. Provisional PatentApplication No. 60/368,286 filed on Mar. 28, 2002.

BACKGROUND

This invention relates to HSDPA in a wireless communication system. Moreparticularly, this invention prevents the losing synchronization for UMRLC when the communication switches to use a smaller TBS size.

The High Speed Downlink Packet Access (HSDPA) between UTRAN and UEs isbased on techniques, such as HARQ (Hybrid Automatic Repeat Request)transmission and reception protocol used on HS-DSCH (High Speed DownlinkShared Channel) and adaptive modulation to achieve high throughput,reduce delay and high peak rates. The new functionality of hybrid ARQand HSDPA scheduling are included in the MAC layer as shown in FIGS. 1,2 and 4.

At the transmitter side—an UTRAN, the HARQ functions are included andcontrolled in a new entity called MAC-hs located in Node B as shown inFIG. 5. Such HARQ functions include a scheduler, HARQ entity, and HARQprocess. A scheduler schedules MAC-hs SDUs for all connected UEs withina cell. The scheduler determines the HARQ Entity and the queue to beserviced and services priority queues. Meantime, the scheduler willindicate each sending MAC-hs PDU with a Queue ID and a TransmissionSequence Number (TSN) to the HARQ entity; the scheduler also schedulesnew transmissions, retransmission, determines a suitable redundancyversion for each transmitted and retransmitted MAC-hs PDU and indicatesthe redundancy version to lower layer.

Next, there is one HARQ entity assigned to an UE in the UTRAN. The HARQentity sets both the Queue ID and the TSN in transmitted MAC-hs PDUs.The TSN will be incremented for each subsequent transmitted MAC-hs PDUon a HS-DSCH. In addition, the HARQ entity determines a suitable HARQprocess to service the MAC-hs PDU and sets the HARQ process identifieraccordingly. Meantime, the UTRAN's HARQ process sets the New DataIndicator for the transmitted MAC-hs PDUs. The system sets the New DataIndicator to the value “0” for the first MAC-hs PDU transmitted by aHARQ process. The system increments the New Data Indicator by one foreach subsequent transmitted MAC-hs PDU containing new data, while itdoes not increment the New Data Indicator if the MAC-hs PDU is aretransmission one.

Furthermore, the MAC layer uses MAC-hs PDU as the basic data structureto communicate with its upper or below layers or between the transmitterand the receiver. FIG. 6 illustrates the detail format of such MAC-hsPDU where a regular MAC-hs PDU includes a MAC-hs header, a plurality ofMAC-hs SDUs and optional padding field. The system uses a variable sizeof PDU for transmission. There is a trade-off between using the largersize of Transport Block Set (TBS) vs. the degree of robust. The systemcan transmit a MAC-hs PDU with its maximum size, which includes maximumnumber of MAC-hs SDUs (Service Data Units) in one PDU under theenvironment of requiring the least degree of robust. When thetransmitting condition changes, the size of PDU, which in turn means thenumber of SDUs carried in one PDU, has to be reduced to ensure a morerobust transmission.

At the receiver, a UE, to support the HARQ protocol, the HSDPA requiresthe support of functionality of HARQ Entity, HARQ process, reorderingbuffers and disassembly Entity. As shown in FIGS. 4 and 5, one UE hasonly one HARQ entity while supports a number of parallel HARQ processes.The HARQ Entity processes the HARQ process identifiers received onHS-SCCH. And based on the HARQ process identifier, the HARQ entityallocates the received MAC-hs PDU to the corresponding HARQ process.

At the same time, if the New Data Indicator of the new received MAC-hsPDU has been incremented compared to the value in the previous receivedtransmission in this HARQ process or this is the first receivedtransmission in the HARQ process, the UE shall replace the datacurrently in the soft buffer for this HARQ process with the receiveddata. On the other hand, if the New Data Indicator is identical to thevalue used in the previous received transmission in the HARQ process,the UE shall combine the received data with the data currently in thesoft buffer for this HARQ process. Later, if the data in the soft bufferhas been successfully decoded and no error was detected, the UE deliversthe decoded MAC-hs PDU to the reordering entity and generates a positiveacknowledgment (ACK) of the data in this HARQ process. Otherwise, the UEshould generate a negative acknowledgment (NAK) of the data in this HARQprocess and report it to the transmitter. Moreover, the UE's HARQprocess processes the Queue ID of the received MAC-hs PDUs and forwardsthe received MAC-hs PDUs to the reordering queue distribution entity.The reordering queue distribution function routes the MAC-hs PDUs to thecorrect reordering buffer based on the Queue ID.

Later, the reordering entity reorders received MAC-hs PDUs according tothe received TSN. MAC-hs PDUs with consecutive TSNs are delivered to thedisassembly function upon reception. MAC-hs PDUs are not delivered tothe disassembly function if MAC-hs PDUs with lower TSN are missing.There is one reordering entity for each Queue ID configured at the UE.The reordering entity can use a Timer based stall avoidance mechanism ora Window based stall avoidance mechanism or both of them to manage itsreordering buffer. Through the disassembly function, the UE shall removeany padding bits if present and the MAC-hs header, then deliver theMAC-d PDUs in the MAC-hs PDU to MAC-d.

Meantime, the system uses several ways to handling its most frequentencountered transmission errors: First, a NACK is detected as an ACK.The NW (Network) starts afresh with new data in the HARQ process wherethe data block is discarded in the NW and is lost. Retransmission of thediscarded data block is left up to higher layers. Second, an ACK isdetected as a NACK. If the network retransmits the data block, the UEwill re-send an ACK to the network. In this case the transmitter sendsan abort indicator by incrementing the New Packet Indicator, thereceiver will continue to process the data block as in the normal case.Third, the NW implements an automatic default NACK return if the systemsets up a threshold to detect lost status message. And last, if a CRCerror happened on the HS-SCCH, UE receives no data and sends no statusreport. If the absence of the status report is detected, NW canretransmit the data block.

Usually, the system uses a tradeoff scheme between the size of TransportBlock Set (TBS) and the degree of robust for data transmission. In theleast robust modulation and coding scheme (MCS) condition within the TTI(Transmission Timing Interval), the system uses the largest TBS size ofMAC-hs PDU to maximum data transmission rate. When radio conditionchanges while a more robust MCS is required for successful transmission,instead of using the largest TBS size of a maximum date rate, the systemhas to switch to use a smaller TBS size for a slower data rate withinthe TTI.

Nevertheless, according to the prior art, every time the system switchesfrom operating at the higher data rate with a larger TBS size to use asmaller size of MAC-hs PDU for a more robust MCS requirement, alloutstanding MAC-hs PDUs in HARQ processes that have not been positivelyacknowledged will be discarded. The discarding of the MAC-hs PDUsdefinitely causes system inefficiency and latency that requires effectsfrom higher layers of the transmitter to recovery these discarded datablocks.

The problems of the prior art can be further illustrated in thefollowing two examples. First, assume that a UE's HARQ entity has sixHARQ processes and is using the largest MAC-hs PDU size fortransmission. Process 1 to 6 transmits MAC-hs PDUs with TSN 0 to 5 to UErespectively. After the first transmission of each process, thetransmitter receives positive acknowledgments for MAC-hs PDUs withTSN=0, 2, 4 and 5 and negative acknowledgments for MAC-hs PDUs withTSN=1 and 3. Before starting the second transmission of each process,due to the change of radio conditions, the system has to use a smallerTBS size for MAC-hs PDU size. According to the prior art, MAC-hs PDUswith TSN=1 and 3 will be discarded, so are dozens of RLC PDUs containedin these two PDUs. If MAC-hs PDUs with TSN=1 and 3 contain RLC UM PDUs,these RLC UM PDUs are lost forever.

Second, again assume that the largest MAC-hs PDU size is used in theMAC-hs PDU and the HARQ entity of an UTRAN allocates six HARQ processesto transmit data to one UE. Each HARQ process is transmitting one MAC-hsPDU and none of them has not received any acknowledgment for itstransmitted MAC-hs PDU. Due to the change of the radio conditions, nowthe MCS must switch to use a more robust MCS that means to use a smallersize of MAC-hs PDU for transmission. According to the prior art, the sixMAC-hs PDUs transmitted without positively acknowledged must be alldiscarded because their sizes does not conform to the new MAC-hs PDUsize. If the six pending MAC-hs PDUs include more than 128 consecutiveUM PDUs all sent by the same UM RLC entity, the HFN synchronization ofthe peer UM entities will be lost. Consequently, all the following UMPDUs will not be deciphered correctly. The prior art has no mechanism inthe RLC layer to handle this serious problem.

SUMMARY

There is a need to modify the prior art to prevent the chance to losethe synchronization of the peer UM entities and to save the systemresource.

BRIEF DESCRIPTION OF THE DRAWINGS

Following drawings with reference numbers and exemplary embodiments arereferenced for explanation purpose.

FIG. 1 illustrates the Protocol Architecture of HSDPA Configuration withMAC-c/sh;

FIG. 2 illustrates the UE side MAC architecture with HSDPA;

FIG. 3 illustrates the UE side MAC architecture/MAC-hs details;

FIG. 4 illustrates the UTRAN side overall MAC architecture;

FIG. 5 illustrates the UTRAN side MAC architecture/MAC-hs details;

FIG. 6 illustrates the MAC-hs PDU format;

FIG. 7 illustrates the logic flowchart of this invention of how toconstruct a new MAC-hs PDU when receives a request to switch to use asmaller size MAC-hs PDU;

FIG. 8 illustrates another logic flowchart of this invention of how toconstruct a new MAC-hs PDU when receives a request to switch to use asmaller size MAC-hs PDU;

DETAIL DESCRIPTION OF THE INVENTION

When a request to switch to use a smaller size of a MAC-hs PDU happens,instead of discarding all unacknowledged MAC-hs PDUs (the unACKed PDU)in the HARQ process as the prior art does, this invention will pickupRLC PDUs of the discarding MAC-hs PDUs affected by the size changerequest in the HARQ process and repackaged them into the new smallersize MAC-hs PDUs that conforms to the new TBS size. So that the newMAC-hs PDU includes at least a subset of the MAC-hs SDUs in the originalMAC-hs PDU before being discarded. Because it is difficult to recoverthe RLC UM PDUs once they are discarded, when pick RLC PDUs from theunACKed PDUs to form the new MAC-hs PDUs (the new PDU), the inventionwill select the RLC UM PDUs over RLC AM PDUs from the unACKed PDU. Thisinvention has two alternative approaches for selecting the RLC UM PDUsover the RLC AM PDUs.

The logical flow of the first approach is shown in FIG. 7. The inventionstarts with one pending unACKed PDU but it will eventually process allunACKed PDUs affected by the size change request through. In the Step 3of FIG. 7, upon receiving a request to switch to use a smaller TBS size.The invention selects one of the unACKed PUDs (Steps 5 and 9), theinvention first checks if the MAC-hs SDUs of the unACKed PDU containsboth RLC UM PDUs and RLC AM PDUs (Step 11), if the SDU does contain bothRLC UM PDUs and AM PDUs, then the invention will pick up the RLC UM PDUsfrom the unACKed PDU and loads them into the smaller size new PDUs (Step19). After loading all RLC UM PDUs if there is more free space availablein the new PDU, then selects more RLC AM PDUs of the unACKed PDU andloads them into the free space of the new PDU until there is no morefree space (Steps 21 and 23). Next, the transmitter assigns the TSN ofthe unACKed PDU to the new PDU and indicates the New Data Indicator asnew for the new PDU (Step 25). Now, as shown in Step 27, this new PDU isready to be transmitted. Of course, if the unACKed PDU contains only RLCUM PDUs or only RLC AM PDUs, then the invention just picks the containsof the unACKed PDU and loads them into the new PDU until it is filled asshown in Steps 13, 15 and 17). Afterward, the new PDU will have the sameTSN of the unACKed PDU and the New Data Indicator for the new PDU isindicated as new (Steps 25 and 27).

Next, refer to FIG. 8, it is the flowchart of the second approach of theinvention. When the system receives a request to use a smaller TBS size(Step 37), this process will apply to all unACKed PDUs affected by thesize change request one at a time by selecting one of unACKed PDUs(Steps 39 and 43). The invention first checks if the MAC-hs SDUs of theunACKed PDU contains both RLC UM PDUs and RLC AM PDUs (Step 45), if theSDU does contain both, then the invention selects at least one RLC UMPDU of each RLC UM entities of the unACKed PDU and loads them into thenew PDU (Step 49). If the new MAC-hs PDU still has free space afterward(Step 59), then selects other RLC UM PDUs and AM PDUs from the unACKedPDU to fill up the rest free space (Step 61). Meantime, assign the sameTSN of the unACKed PDU to the new MAC-hs PDU while indicates the NewData Indicator for the new PDU as new (Step 63). Now, as shown in Step65, this new PDU is ready to be transmitted. Then the same or adifferent HARQ process can be scheduled to transmit the new MAC-hs PDUwith the PDU's New Data Indicator indicated as new. One way used toindicate the New Data Indicator as new is to set the New Data Indicatorto the value “0” for the new MAC-hs PDU if the new MAC-hs PDU is thefirst MAC-hs PDU transmitted by a HARQ process and increment the NewData Indicator for the new MAC-hs PDU if the new MAC-hs PDU is not thefirst MAC-hs PDU transmitted by a HARQ process. If the unACKed PDUcontains only RLC UM PDUs (Step 47), then this invention will extract atleast one RLC UM PDU for each UM Entity and loads them into the new PDU(Step 51). Furthermore, if there is more free space left in the new PDUthen extracts more RLC UM PDUs from the unACKed PDU and loads them intothe new PDU until the new PDU is filled (Step 57). Meantime, if theunACKed PDU contains only RLC AM PDUs, then the invention extracts RLCAM PDUs and load them into the new PDU until the new PDU is filled(Steps 53, 55 and 57.) The new PDU will have the same TSN of the unACKedPDU and the New Data Indicator for the new PDU is indicated as new (Step63). Then this new PDU is ready to be transmitted (Step 65).

This invention will prevent losing more than 128 consecutive UM PDUsbelonging to a RLC UM entity during the switch. Therefore, the problemof HFN lost synchronization is avoided in the second example. Moreover,for example, a MAC-hs PDU with its TSN=100 that being transmitted in theHARQ process contains 10 RLC UM PDUs from one RLC UM entity and 20 RLCAM PDUs. Before this MAC-hs PDU is positively acknowledged, a morerobust MCS is requested to switch to use a smaller size of MAC-hs PDU.This MAC-hs PDU needs to be reconstructed to a smaller MAC-hs PDU toconform to the new MCS requirement. If the new MAC-hs PDU can onlycontain 15 RLC PDUs, a subset of 30 RLC PDUs in the original MAC-hs PDUcan be included in this new PDU. By using the first approach, the 15 RLCPDUs within the new MAC-hs PDU contain 10 RLC UM PDUs and 5 RLC AM PDUs.This new MAC-hs PDU is sent with the same TSN=100 and the associated NewData Indicator indicated as new. By using the second approach, at leastone of the RLC UM PDUs is contained in the new MAC-hs PDU and the otherspace (14 PDUs) can be filled by the rest RLC UM PDUs and RLC AM PDUsaccording to the priority of the RLC entities.

1. A method to prevent HFN unsynchronization for UM RLC between atransmitter and a receiver in HSDPA of a high speed wirelesscommunication system; wherein the transmitter assigns a TransmissionSequence Number (TSN) to each sending data package and temporarily keepsthe sent data package until receiving a corresponding response from thereceiver, meanwhile due to the change of the communication condition,the system switches to use different sizes of data package—MAC-hs PDUfor transmitting, the method comprising the steps of: at thetransmitter: receiving a request to switch using a smaller size datapackage, a new MAC-hs PDU to be transmitted; until all unacknowledgedMAC-hs PDUs have been processed, processing everyone of theunacknowledged MAC-hs PDUs affected by the size change request one at atime with the following steps a to f; a. extracting subsets from thecontains of the unacknowledged MAC-hs PDU; b. filling up the new MAC-hsPDU with the extracted subsets; c. assigning the TSN of theunacknowledged MAC-hs PDU to the new MAC-hs PDU; d. indicating the newMAC-hs PDU containing new data; e. discarding the extractedunacknowledged MAC-hs PDU; and f. putting the new MAC-hs PDU ready to betransmitted.
 2. The method as claimed in claim 1, wherein the extractedsubsets are RLC PDUs containing either RLC UM PDUs or RLC AM PDUs orboth of them.
 3. The method as claimed in claim 2, wherein indicatingthe new MAC-hs PDU containing new data comprising the steps of: settingthe value of the New Data Indicator to the value “0” for the new MAC-hsPDU if the new MAC-hs PDU is the first MAC-hs PDU transmitted by a HARQprocess; incrementing the value of the New Data Indicator with one forthe new MAC-hs PDU if the new MAC-hs PDU is not the first MAC-hs PDUtransmitted by a HARQ process; and assigning the value to the New DataIndicator to the new MAC-hs PDU.
 4. The method as claimed in claim 2,extracting subsets from the unacknowledged MAC-hs PDU further comprisingthe steps of: selecting the RLC UM PDUs first if the unacknowledgedMAC-hs PDU containing such PDUs; and selecting the RLC AM PDUs if thenew MAC-hs PDU has free space and if the unacknowledged MAC-hs PDUcontaining no RLC UM PDU or all UM PDUs have been extracted.
 5. Themethod as claimed in claim 2, extracting subsets from the unacknowledgedMAC-hs PDU further comprising the steps of: selecting at least one RLCUM PDU from every UM entity first if the unacknowledged MAC-hs PDUcontaining either both RLC UM PDUs and RLC AM PDUs or RLC UM PDUs only;afterward selecting RLC PDUs from the rest of the unacknowledged MAC-hsPDU whether they are the RLC UM PDUs or the RLC AM PDUs if the newMAC-hs PDU has free space; and selecting the RLC AM PDUs if theunacknowledged MAC-hs PDU containing only RLC AM PDUs and if the newMAC-hs PDU has free space.
 6. The method as claimed in claim 5, whereinafterward selecting RLC PDUs further comprising of selecting RLC PDUsbased on their priority.
 7. A system having means for preventing HFNunsynchronization for UM RLC between a transmitter and a receiver inHSDPA of a high speed wireless communication system; wherein thetransmitter assigns a Transmission Sequence Number (TSN) to each sendingdata package and temporarily keeps the sent data package until receivinga corresponding response from the receiver, meanwhile due to the changeof the communication condition, the system switches to use differentsizes of data package—MAC-hs PDU for transmitting, where the transmittercomprising: means for receiving a request to switch using a smaller sizedata package, a new MAC-hs PDU to be transmitted; means for processingevery unacknowledged MAC-hs PDUs affected by the size change request;means for extracting subsets from the contains of the unacknowledgedMAC-hs PDU; means for filling up the new MAC-hs PDU with the extractedsubsets; means for assigning the TSN of the unacknowledged MAC-hs PDU tothe new MAC-hs PDU; means for indicating the new MAC-hs PDU containingnew data; means for discarding the extracted unacknowledged MAC-hs PDU;and means for putting the new MAC-hs PDU ready to be transmitted.
 8. Thesystem as claimed in claim 7, wherein means for extracting subsets wheresubsets are RLC PDUs containing either RLC UM PDUs or RLC AM PDUs orboth of them.
 9. The system as claimed in claim 8, wherein means forindicating the new MAC-hs PDU containing new data further comprising:means for setting the value of the New Data Indicator to the value “0”for the new MAC-hs PDU if the new MAC-hs PDU is the first MAC-hs PDUtransmitted by a HARQ process; means for incrementing the value of theNew Data Indicator with one for the new MAC-hs PDU if the new MAC-hs PDUis not the first MAC-hs PDU transmitted by a HARQ process; and means forassigning the incremented value to the New Data Indicator to the newMAC-hs PDU.
 10. The system as claimed in claim 8, means for extractingsubsets from the unacknowledged MAC-hs PDU further comprising: means forselecting the RLC UM PDUs first if the unacknowledged MAC-hs PDUcontaining such PDUs; and means for selecting the RLC AM PDUs if the newMAC-hs PDU has free space and if the unacknowledged MAC-hs PDUcontaining no RLC UM PDU or all UM PDUs have been extracted.
 11. Thesystem as claimed in claim 8, means for extracting subsets from theunacknowledged MAC-hs PDU further comprising: means for selecting atleast one RLC UM PDU from every UM entity first if the unacknowledgedMAC-hs PDU containing either both RLC UM PDUs and RLC AM PDUs or RLC UMPDUs only; means for selecting RLC PDUs afterward from the rest of theunacknowledged MAC-hs PDU whether they are the RLC UM PDUs or the RLC AMPDUs if the new MAC-hs PDU has free space; and means for selecting theRLC AM PDUs if the unacknowledged MAC-hs PDU containing only RLC AM PDUsand if the new MAC-hs PDU has free space.
 12. The system as claimed inclaim 11, wherein means for selecting RLC PDUs afterward furthercomprising of selecting RLC PDUs based on their priority. A transmitterhaving means for preventing HFN unsynchronization for UM RLC with areceiver in HSDPA of a high speed wireless communication system; whereinthe transmitter assigns a Transmission Sequence Number (TSN) to eachsending data package and temporarily keeps the sent data package untilreceiving a corresponding response from the receiver, meanwhile due tothe change of the communication condition, the transmitter switches touse different sizes of data package—MAC-hs PDU for transmitting, wherethe transmitter comprising: means for receiving a request to switchusing a smaller size data package, a new MAC-hs PDU to be transmitted;means for processing every unacknowledged MAC-hs PDUs affected by thesize change request; means for extracting subsets from the contains ofthe unacknowledged MAC-hs PDU; means for filling up the new MAC-hs PDUwith the extracted subsets; means for assigning the TSN of theunacknowledged MAC-hs PDU to the new MAC-hs PDU; means for indicatingthe new MAC-hs PDU containing new data; means for discarding theextracted unacknowledged MAC-hs PDU; and means for putting the newMAC-hs PDU ready to be transmitted.
 14. The transmitter as claimed inclaim 13, means for extracting subsets from the unacknowledged MAC-hsPDU further comprising: means for selecting at least one RLC UM PDU fromevery UM entity first if the unacknowledged MAC-hs PDU containing eitherboth RLC UM PDUs and RLC AM PDUs or RLC UM PDUs only; means forselecting RLC PDUs afterward from the rest of the unacknowledged MAC-hsPDU whether they are the RLC UM PDUs or the RLC AM PDUs if the newMAC-hs PDU has free space; and